ZBB - 0 bug 反弹 - zero bug bounce
ZBB是指在项目中的某一点上，开发活动最终赶上了测试的步伐，当前已经不存在活跃bug。在ZBB之后，bug数量的峰值将显著减小，并且bug数量会持续减少直到产品足够稳定，进而构建出第一个候选发布版。取得ZBB是项目组逐渐接近稳定的候选发布版的明确标志。
Every build (for a CTP, RC, etc.) starts with a bunch of improvements and defects. We start troubleshooting them and find bugs. We then start fixing bugs. When a particular build has no more active bugs in it, we say it's a ZBB. As the product develops in time, we add more features/defects/improvements to it, which means more bugs discovered (ZBB <> 0) and we go about fixing these bugs (ZBB = 0).
Officially: A point in time at which a given segment of reported bugs is driven down to zero Active. Since real-time zero is unrealistic to track or hit, often ZBB is postfixed with a number is used to indicate age in days of oldest bugs you may have in the system. For example, ZBB-7 states that there should be no Active bug reports older than 7 days. This is typically calculated per component team and is used when attempting to drive a product to lock-down for ship